This invention is in the field of hand held drills and more specifically dental tools. Dental drills are driven either by a belt pulley combination or by means of pressurized fluid directed against a rotatably mounted tubine having the dental tool mounted thereon. In either case, the hand piece must be connected to a remote source of energy either by flexible conduits having the pressurized fluid therein or by belts. Another approach is to rotate the drill by means of a miniature motor mounted in the head of the hand piece with the motor then being connected by wires to a remote source of electrical energy. An example of an air driven motor located in the hand piece is shown in U.S. Pat. No. 4,040,311 and Re. 28,649. An earlier version is shown in U.S. Pat. No. 77,370 wherein the air motor is driven by compressed air operated by a foot-bellows.
Modern dental hand pieces rotate the dental drill at speeds in excess of 250,000 rpm. As a result, the source of driving energy is located remotely from the hand piece particularly since the hand piece must be very compact and easy and convenient for a dentist to manipulate. On the other hand, the various connections required between the dental hand piece and the remote source of energy limits the freedom of movement of the dentist while also necessitating various hoses, wires or belts in the area of the patient's mouth. These problems have been solved by the design of the dental hand piece disclosed herein which has a rechargeable self-contained energy source. Through the utilization of an expansion chamber and constrictor, a charge of pressurized liquid is contained within the handle of the hand piece with the liquid then changing to a pressurized gas for driving the tool providing a very efficient source of energy.